how to i find average speed?
the problem says.
a driver set outa journey for the first half she drives at 30mi/h and second half 60mi/h. Find the driver's average speed?
This is a trick question. The answer depends upon whether she drove half the TIME at each speed or half the DISTANCE at each speed. Let's assume that half of the DISTANCE was driven at 30 mi/h and the other half at 60 mi/h.
To get the average speed in either case, divide the total distance by the total time required.
If L is the total distance in miles, the total time required is
(L/2)/30 + (L/2)/60
and the average speed is
L/[(L/2)/30 + (L/2)/60]
= 1/[1/60 + 1/120) = 1/(3/120)
= 40 mi/h